1. Field of the Invention
The present invention relates to a display panel device, and more particularly to a method and apparatus for data-driving an electro-luminescence display panel device.
2. Description of the Related Art
Currently, various flat panel displays are being developed to have reduced weight and overall size to replace cathode ray tube (CRT) devices. These flat panel displays include liquid crystal display (LCD) devices, field emission display (FED) devices, plasma display panel (PDP) devices, and electro-luminescence display (ELD) devices. Accordingly, these flat panel display devices can be classified into voltage drive devices and current drive devices.
The ELD devices are self-luminous, wherein fluorescent materials emit light by re-combining electrons with holes. The ELD devices have fast response speeds, as compared to CRT devices and passive-type luminous devices that require separate light sources, such as the LCD devices. The ELD devices may be considered current drive-type and voltage drive-type, and can generally be classified into inorganic ELD and organic ELD devices in accordance with their materials and structures.
FIG. 1 is a schematic cross sectional view of an organic electro-luminescence display device according to the related art. In FIG. 1, an organic ELD device includes an electron injection layer 4, an electron transport layer 6, a light emission layer 8, a hole transport layer 10, and a hole injection layer 12 that are deposited between a cathode 2 and an anode 14. If a voltage is supplied between the anode electrode 14 of a transparent electrode material and the cathode electrode 2 of a metal electrode material, electrons generated from the cathode 2 move toward the light emission layer 8 through the electron injection layer 4 and the electron transport layer 6. Furthermore, holes generated from the anode 14 move toward the light emission layer 8 through the hole injection layer 12 and the hole transport layer 10. Accordingly, the electrons and the holes supplied from the electron transport layer 6 and the hole transport layer 10 collide in the light emission layer 8 to re-combine, thereby generating light that is emitted through the anode 14 to an exterior to display an image. A luminous brightness of the ELD device is not proportional to a voltage supplied to both ends of the device, but is proportional to a supply current. Thus, the anode 14 is normally connected to a constant current source.
FIG. 2 is a schematic plan view of an active matrix-type electro-luminescence display device according to the related art. In FIG. 2, an active matrix-type ELD device includes an ELD panel 16 having a pixel 22 arranged at each intersection part of scan lines SL and data lines DL, a scan driver 18 to drive the scan lines SL, and a data driver 20 to drive the data lines DL. Each of the pixels 22 are selected when scan pulses are supplied to the scan line SL of a cathode to generate light corresponding to a pixel signal, i.e., a current signal supplied to the data line DL of anode. The pixels 22 include an electro-luminescence (OEL) cell and a cell driver. Each OEL cell may be equivalently expressed as a diode connected between the data line DL and the scan line SL, wherein each OEL cell emits light when a negative scan pulse is supplied to the scan line SL and a positive current is simultaneously supplied to the data line DL in accordance with a data signal, thereby supplying a forward voltage. Alternatively, a reverse voltage is supplied to the OEL cell included in an unselected scan line, whereby no light is emitted. In other words, the light-emitting OEL cell is charged with a forward charge, whereas the OEL cell with no light emission is charged with a reverse charge.
The scan driver 18 sequentially supplies the negative scan pulse to scan lines SL, and the data driver 20 supplies a current signal to the data lines DL, wherein the current signal has a current level or pulse width corresponding to a data signal for each horizontal period. Accordingly, the ELD device supplies the current signal with the current level or pulse width proportional to input data to the OEL cell, and each OEL cell emits light in proportion to the amount of current applied from the data line DL.
FIG. 3 is a schematic circuit diagram of a data driver shown in FIG. 2 according to the related art. The data driver 20 controls the pulse width of the current signal in response to the input data, and includes a plurality of data drive integrated circuits (ICs) and a data drive IC 21, which mainly uses a current mirror circuit in order to create a constant current.
In FIG. 3, the data driver IC 21 includes a reference MOSFET M0 connected between a voltage source VDD and a ground voltage source, wherein the constant current sources, i.e., constant current supply MOSFETs M1 to M4 that are connected to the voltage source VDD and, at the same time, connected in parallel to the reference MOSFET M0, form a current mirror circuit for supplying the constant current (i) to each data line connected to the OEL cell 24. In addition, the data drive IC 21 includes switch devices S1 to S4 that are connected between the constant current supply MOSFET M1 to M4 and the data line to control a supply time of the constant current (i) from the constant supply MOSFET M1 to M4 in response to the input data, thereby controlling the pulse width of the current signal. Accordingly, it is possible for the data drive IC 21 not to include the switch devices S1 to S4.
Each of the constant current supply MOSFETs M1 to M4 together with the reference MOSFET M0 receive the supply voltage of the voltage source VDD in parallel to form a current mirror circuit with the reference MOSFET M0. Accordingly, the same amount of constant current (i) or 2n times the constant current, i.e., 2i, 4i, 8i, . . . , is supplied. The constant current (i) supplied from the constant current supply MOSFETs M1 to M4 changes in accordance with the amount of load, i.e., line resistance, of the data lines and capacitance that are both related to the amount of light emission of the OEL cell 24 due to the structure of the ELD panel. Accordingly, the data drive IC 21 includes a plurality of current control resistors each having resistance values different from each other in order to control the changing current in accordance with the amount of load. In addition, a resistor is selected among the plurality of current control resistors in accordance with an average amount of load of the data drive IC 21 to be connected between the reference MOSFET M0 and ground, thereby controlling the constant current (i) of the data drive IC 21.
The data driver 20 includes a plurality of data drive IC's 21, as shown in FIG. 3. In addition, another reference current source to the external voltage source is required for each data drive IC 21 to supply the reference current to the reference MOSFET M0. Accordingly, the output of each reference current source needs to be equal in order to reduce the current output deviation between the data drive IC's 21. Thus, each data drive IC 21 uses the same external voltage source VDD, and each current source needs to be adjusted for equalizing the reference current.
However, the active matrix-type ELD device has its own problems. For example, when the number of reference current sources increases, more operational time is required to adjust the reference current sources when a plurality of data drive IC's 21 are used.